Motivation
On most foreign language or multilingual Drupal 8 sites there will at least be views in 2 different languages, the English views shipped with Drupal core and the Views created on the site for the site's foreign language. On multilingual sites, it is possible there will be views that do not apply to all languages and therefore only created in specific languages (although that is more of an edge case).
The shipped views are in English and they should say so in their configuration yml files. See #1935000: Some configuration entities are created as in language unknown which covers views.
However when users edit/create views, we should give them the ability to specify the language for their views. Why is this important? Well, only English shipped views are translated with the localize.drupal.org .po file system. Second, knowing which source language is used lets the configuration translation system offer it up for translation in other languages.
As an example in core, vocabulary config entities already have a language selector for the same reason (the tags shipped vocabulary is also English).
I think on the Views UI this would likely belong in the "edit name/description" popup screen, because those are the high level properties of the view.